Over the past 20 years, the morphology of the Lingding Bay in the Zhujiang River Estuary has undergone anomalous changes, which is far beyond natural processes due to the influence of high intensity human activities. Hence, the resulted estuarine dynamics have inevitably influenced as well as the material transport processes. In this study, a three-dimensional model has been setup to explore the changes of residual circulation pattern in the Lingding Bay over the past 20 years and their potential impacts. The results show that the bottom residual flow along the East and West channels is turned towards the Middle Shoal area, which promotes the sedimentation there. The lateral residual circulation in the Middle Shoal depicts a layered structure of the surface to the west and the bottom to the east, mainly driven by the non-linear advection term. The large-scale sand mining in the Middle Shoal has resulted in the eastward shift of the residual circulation structure and the enhancement of the surface and bottom residual currents, which can accelerate the exchange of material between the surface and bottom layers. A longitudinal residual circulation structure exists in the West Channel with the surface layer seaward and the bottom layer landward, driven mainly by barotropic and baroclinic pressure gradient forces. Due to the effect of dredging depth, both the landward baroclinic pressure gradient force and the non-linear convection term are enhanced, the seaward-direction surface residual flow reduces by 22%, while the landward-direction bottom residual flow increases by 24%, which will weaken the exchange capacity of the water body in the western trough during the neap tide period, i.e. slow down the material export, resulting in the siltation of the western trough and the weakening of the water environment. This study can provide implications for understanding of estuarine residual circulation as well as material transport under anthropogenic disturbance.

In order to investigate the melting process at the ice-water lateral interface and to quantify the dominant factors affecting the lateral melting rate of ice layer, an ice melting experiment was carried out in a low-temperature water tank. Simultaneous measurements of the ice bottom and surface processes and the lateral melting process of the ice layer were carried out, while the laboratory air temperature, ice temperature at different depths inside the ice samples and water temperature at different depths in open water were recorded, the relationships between different elements and their influence patterns on the lateral melting rate of ice were investigated using correlation analysis methods. The results show that the lateral melting rate at different depths inside the ice samples was slow and uniform in the early stage of melting, with an average melting rate of 0.05 mm/h. The lateral melting rate at different depths in the middle and late stages of melting increased significantly and was no longer uniform, with an average melting rate of 0.15 mm/h. The correlation coefficient of the average lateral melting rate and air temperature (r=0.82) was better than that between the average water temperature (r=0.74) and the water-ice temperature difference (r=0.48). The quantitative relationships of lateral melting rate with temperature (air temperature, water temperature) and depth were established to accurately describe the non-uniformity of the lateral melting process of ice layer. It also verifies the feasibility of conducting non-uniform lateral melting test techniques, and lays the foundation for sea ice tests that more closely resemble real Arctic conditions considering wind speed and light source conditions.

The short wave radiation budget on the sea surface is an important physical process of energy exchange at the sea-air interface. In this study, the sea surface short wave radiation flux budget of ERA5 reanalysis data is evaluated by using the observed data of summer scientific research voyages in the northern South China Sea in 2019. The results show that the downward short wave radiation of ERA5 is smaller than the observed data, and the deviation is the largest at 11:00 and 15:00 (Beijing time), up to −100 W/m². At the same time, the sea surface albedo of ERA5 is generally lower than observed. The bias in ERA5 is small under a high solar altitude angle, being about −0.03, but can reach −0.15 under a low solar altitude. The bias in the downward shortwave radiation and sea surface albedo jointly caused an underestimation of 25.4 W/m² in the daytime average sea surface net shortwave radiation flux in ERA5. In particular, the albedo underestimation offsets about 50% of the contribution of downward shortwave radiation bias. The results show that ERA5 has different manifestations of sea surface radiation budget deviation under different atmospheric transmittance conditions. We also found that the underestimation of sea surface albedo in ERA5 is caused by its parameterization schemes and put an optimization based on our observation.

In order to clarify the genetic mechanism of shallow continental shelf sandbodies in the upper submember of the first member of Zhujiang Formation in the northwestern Zhusan Depression, with integrated use of geological and geophysical data, the five-order sequence framework was established firstly, inside of which, the shallow continental shelf sandbodies were identified and quantitatively described, and the temporal and spatial evolution of the shallow continental shelf sandbodies were analyzed, and the genetic mechanism was discussed. The results show that: (1) The upper submember of the first member of Zhujiang Formation in the study area can be divided into four five-order sequences, which were numbered as FS4, FS3, FS2 and FS1 from bottom to top. (2) There are two types of shelf sand bodies: tidal sand ridge and offshore sand bar, which are distributed in NW−SE direction. Tidal sand ridges are mainly distributed in the west of the study area, while offshore sand bars are concentrated in the east. (3) In the three five-order sequences FS4, FS3 and FS2, the scale and quantity of both tidal sand rdiges and offshore sand bars are relatively large, while in the upper five-order sequence FS1, the scale and quantity present poor. (4) Sedimentary base level (hydrodynamic condition), synsedimentary geomorphology and sediment debris supply jointly affected the development scale, distribution characteristics and temporal and spatial evolution of tidal sand ridges and offshore sand bars, which comprehensively constituted the genetic mechanism of shallow continental shelf sand bodies in the northwestern Zhusan Depression.

Paleoclimate and paleoenvironment reconstruction based on shelf mud deposits remain controversial due to the complexity of coastal dynamic conditions. In this paper, three sediment cores distributed along the sediment transport path in the North Yellow Sea were collected, and the sediment grain size composition, end member, winter storms and Yellow Sea Warm Current strength variation were also analyzed. Based on above analysis, the response mechanism and intensity of different sediment grain size end member to winter storms and Yellow Sea Warm Current were discussed, and sedimentary effect in different regions caused by the above changes was also revealed. The results show that sediment composition in the north branch of Huanghe River distal mud is dominated by the natural condition and human activity over the past 100 years, respectively. Due to the impact of human activities on the sediment flux and composition of the Huanghe River into the sea began to enhance since 1980, and the natural evolution information was destroyed. In addition, through comparing sediment end member of different cores along the sediment transport pathway, the discrepancy in response mechanism and intensity of different end member to winter storms and the Yellow Sea Warm Current were observed before 1980, which reflected significant regional sedimentation effect. Further analysis demonstrated that, the coarse-grained end member is dominated by the winter storm, reflecting intensity of cross-front transport from the north Shandong Peninsula; and the fine-grained end member is controlled by the Yellow Sea Warm Current, representing the long distance transport from the offshore mud patch of the western North Yellow Sea to the eastern coast of the Liaodong Peninsula. Above conclusions indicated that, the sediment grain size is a robust tool for paleoclimate and paleoenvironment reconstruction; however, the utility of sensitive grain size should be based on sediment source and the characteristics of the sediment hydrodynamic environment analysis, and selection of the sensitive grain size and its implication should be careful.

This article is focus on the distribution and source of organic matter in tidal flat in the Jiulong River Estuary, and to seek effective organic geochemistry proxies for recognize sedimentary microfacies, and thus to help that organic carbon is better applied to identify sedimentary microfacies and paleo-environment. Forty one surficial sediment samples were obtained and measured their grain size, total organic carbon (TOC), total nitrogen (TN), and organic carbon stable isotopes (δ¹³C) in the tidal flat from three sedimentary environments: upper tidal flat, middle tidal flat and lower tidal flat in summer and winter. The results show that, from upper tidal flat to lower tidal flat, the grain size of sediments becomes coarser gradually with decreasing TOC, TN and C/N, and the increase of δ¹³C. The sources of organic matter in the upper tidal flat are dominated by terrestrial organic matter and mangrove, marine organic matter and Spartina alterniflora in middle tidal, and marine organic matter in lower tidal flat. The distribution and sources of organic carbon in tidal flat from the Jiulong River Estuary are controlled by the seasonal changes of land-ocean interaction, sedimentary hydrodynamic sorting, and plants. There is a significant difference in TOC, and a highly significant difference in TN and δ¹³C in sediments of the tidal flat. We thus proposed that organic geochemistry properties TOC, TN and δ¹³C are the effective indicators to identify upper tidal flat and middle-lower tidal flat in the Jiulong River Estuary.

Little research attention has been paid to comparison of the descriptive terms used in graphical method and moment method for grains-size parameters, although some work has been done on comparison of the numerical values and mutual conversion equations. In this paper, 105 surface sediments from 22 sections of 15 beaches on both sides of the Qiongzhou Strait are selected as typical research objects. The grain-size parameter results are obtained by the Folk & Ward graphic method and Friedman moment method respectively. The regression relationship of quantitative results is constructed and the similarities and differences of qualitative results are compared. Combined with the previous research results, this paper further discusses the comparability of the results of the two methods, and analyzes the possible impact of the differences between the two methods on the extraction and use of sediment particle size information. The results show that: (1) in terms of quantitative results, the average particle size and sorting coefficient calculated by graphic method and moment method have strong correlation (R² ≥ 0.951), while the skewness and kurtosis show moderate correlation (R² = 0.586) and uncorrelation (R² = 0.011), indicating that the correlation between the quantitative results of particle size parameters calculated by the two methods is not stable, which is basically consistent with the previous research results; (2) as far as qualitative results are concerned, there is a large deviation between the results of graphic method and moment method. The proportion of inconsistent sorting coefficient, skewness and kurtosis is 30.48%, 55.24% and 71.43% respectively, which deviates from the correlation of quantitative results to a certain extent, indicating that the correlation degree of quantitative results can not be fully used to indicate the consistency degree of qualitative term results. Since it is the goal of grain-size parameter analysis method to reveal the differences of sediments to the greatest extent, it is necessary to fully consider the characteristics of grain-size distribution curve when choosing which method to calculate grain-size parameters. This paper provides a typical case of comparing the results of graphical method and moment method for grain-size parameters of beach sediments. The research results help to improve the understanding of the differences, causes and scientific use of grain-size parameter analysis methods.

To provide technical support for sea ice environmental monitoring and dynamic risk early warning in the sea area of the proposed, under construction and built cold source water intake project in cold regions, a Lagrangian particle tracking prediction model under the sea ice ocean coupling condition is constructed in this paper. Taking the water intake of a nuclear power station in the Liaodong Bay as an example, the migration trajectories of high-risk ice blocks in 24 h, 48 h and 72 h under cold wave weather and the probability of entering the water intake are simulated and discussed. The results show that since the direction of the water intake is almost perpendicular to the flow direction and wind direction, less than 6% of the 1200 high-risk ice particles randomly released outside the water intake enter the water intake. It is found that most of the particles come from within 300 m near the water intake by identifying the particle color in different regions. The results of sensitivity analysis showed that when the number of released particles increased to 5 times, the conclusion remained unchanged. This study provides a new method for safety early warning of cold source water intake.

The delimitation and naming of seabed geographic entities is one of the hot research issues in the field of international maritime rights and interests. However, due to the lack of quantitative definition technology for the boundaries of seabed geographic entities, the determination of the boundaries is inevitably artificial. For this reason, this paper proposes a method for the boundary delineation of seabed geographic entities based on the D-P algorithm and optimal path. Convert the high-resolution bathymetry model into a two-dimensional bathymetry matrix, conduct cross-section analysis from the horizontal and vertical directions, and use extreme point simplification and D-P algorithm for quadratic simplification. In this way, the automatic division of the mountain body and its base of a single seamount is realized; on this basis, the method of path optimization is used to realize the automatic segmentation of conjoined seamounts. The method has been verified in the delineation of seabed geographic entities in the South China Sea and achieved good application results.

The multi-beam echo sounder is usually used in bathymetry activity, the accuracy of temperature, salinity and depth profile data play a very important role in the bathymetry. Unfortunately, those errors among the temperature, salinity and depth data were inevitably brought into the measurement. To analyze the influence of temperature, salinity and depth variations on beam footprint coordinates and quantify its influence value, then, on basis of the indirect measurement data of sound velocity profile, the empirical formula of sound velocity with high precision and strong adaptability were selected to deduce their error formula, and the error value of sound velocity caused by temperature, salinity and depth variation was calculated. On the basis of constant-gradient sound ray tracing model, the horizontal and vertical displacement error formulas of sound wave travel path were derived, and then the influence value of acoustic velocity error on beam footprint coordinates was calculated by combining with sound velocity profile. The experimental results show that temperature has the greatest influence on sound velocity, followed by salinity and depth. The variations of temperature, salinity and depth cause the Z-coordinate variation of the beam footprint to be larger than the X and Y coordinates, up to 0.6% of the depth before the change. The variation of three-dimensional coordinates caused by temperature and salinity decreases with the increase of incident angle, however, the variation of three-dimensional coordinates caused by depth hardly changes with the change of incident angle. The results of this paper can be used for reference to evaluate the accuracy of multi-beam bathymetry with temperature, salinity and depth error.